2017 (Gen 7) edit: this combination hits 717 Pokemon for super effective damage and 191 for normal damage as of Sun/Moon. Note, this question was originally posted in 2013.

Fire, Electric, Fighting, and Ground
0 - No Effect
0 - Not Very Effective
179 - Normal Effectiveness
595 - Super Effective
This is the best, I believe, and Infernape also has this movepool. Just use Flare Blitz instead of Acrobatics
Source: http://pokemondb.net/tools/type-coverage

I was trying to find a good type coverage for Dunsparce and I found a really amazing one
Fire+electric+ice+ground
0 no effect
232 regular
676 super effective
Fire+ground+ice+ghost has 640 super effective
There was also a combo with 674 super effective but unfortunately I can't remember what it was